While the present invention is primarily concerned with the injection of fuel into diesel engines, it could be employed in the fuel injection of other internal combustion engines. A common practice for the injection of fuel into the cylinder of a diesel engine is to use a fuel injection valve which substantially corresponds to a pressure relief valve. A high pressure fuel injection pump produces a pressure impulse in the fuel supply line for each cylinder. For a period of time determined by the characteristics designed into the engine, this pressure impulse causes the fuel injection valve to open and remain open while the fuel charge is being injected into the combustion chamber of the engine. As the pressure drops off at the end of the impulse it ultimately reaches a point at which it is no longer sufficient to hold the injection valve open, with the result that the valve closes shutting off the delivery of fuel.
Upon the drop in delivery pressure at the pump at the end of the pressure impulse a shock wave is produced in the fuel line upstream of the injection valve. The shock wave is caused by the inertia of the column of fuel that was moving just prior to the valve's subsequent closing, and may be likened to a shock wave that causes water hammer in a water pipe when a faucet is suddenly closed. Such a shock wave can be sufficient in strength as it reverberates through the length of the fuel supply line to overcome the closing force of the fuel injection valve and consequently cause that valve to briefly reopen. Of course when the fuel injection valve opens in response to such a spurious pressure injection signal, fuel is undesirably introduced into the combustion chamber. The injection of unwanted fuel into the combustion chamber obviously is wasteful. Furthermore, it may be injected at a time such that it is not adequately burned with the result of increasing pollution, etc.
In many diesel engines, a relatively high pressure is employed to open the fuel injection valve with the aim of improving the atomization of the fuel in the combustion chamber. Such pressures may be, for example, in the neighborhood of thirty-five hundred pounds per square inch. To the extent that higher pressures are employed, the more serious is the afterclosing shock waves in the fuel supply leading to the injection valve.
Thus, the principal object of the present invention is to eliminate the reopening of the valve in response to or spurious pressure impulses from the fuel supply lines communicating with the fuel injection valves. This goal is not a novel one, but my procedure for achieving the goal is novel. One prior art practice has been to incorporate a bleed valve into the fuel pump to open the conduit, which leads from the fuel pump to the fuel injection valve, to a by-pass line back to the fuel supply. This by-pass line may also have a pressure absorber connected thereto. See, for example, U.S. Pat. No. 3,587,547.
In the present invention, an electrically operated by-pass or relief valve actually located at the fuel injection valve is opened at the conclusion of the fuel injection impulse. Since this pressure relief valve is at the fuel injection valve end of the fuel supply passage, its opening provides a flow passage through which any such reflected pressure waves arriving at the fuel injection valve are diverted and dissipated to pressure levels insufficient to cause the reopening of the fuel injection valve. Such a relief valve can advantageously be incorporated into an electrically operated system for electronically controlling the fuel charge to the combustion chamber, but need not necessarily be.
In some embodiments of the invention, the relief or by-pass valves at all the injection valves open simultaneously into a common manifold. This ensures that all of the fuel injection valves have a common pressure when they are idle, i.e., the fuel injection pressure build-up starts from a common datum. The result is that uniform quantities of fuel are injected into each of the cylinders by each pressure pulse. If the starting pressures in each of the fuel injection valves are not uniform, i.e., they start from different datums, the quantity of fuel injected will likewise be unequal. This is, of course, an undesirable situation, but one that can occur.
Other objects and advantages will be apparent from the following description taken in conjunction with the drawings.